Exploring, drilling and completing hydrocarbon and other wells are generally complicated, time consuming and ultimately very expensive endeavors. As a result, over the years well architecture has become more sophisticated where appropriate in order to help enhance access to underground hydrocarbon reserves. For example, as opposed to wells of limited depth, it is not uncommon to find hydrocarbon wells exceeding 30,000 feet in depth. Furthermore, as opposed to remaining entirely vertical, today's hydrocarbon wells often include deviated or horizontal sections aimed at targeting particular underground reserves.
While such well depths and architecture may increase the likelihood of accessing underground hydrocarbons, other challenges are presented in terms of well management and the maximization of hydrocarbon recovery from such wells. For example, during the life of a well, a variety of well access applications may be performed within the well with a host of different tools or measurement devices. However, providing downhole access to wells of such challenging architecture may require more than simply dropping a wireline into the well with the applicable tool located at the end thereof. Indeed, a variety of isolating, perforating and stimulating applications may be employed in conjunction with completions operations.
In the case of perforating, different zones of the well may be outfitted with packers and other hardware, in part for sake of zonal isolation. Thus, wireline or other conveyance may be directed to a given zone and a gun assembly with related and/or controlling tools employed to create perforation tunnels through the well casing. As a result, perforations may be formed into the surrounding formation, ultimately enhancing recovery therefrom.
The described manner of perforating can be accompanied by a significant degree of ‘gun shock’. That is, as the gun is fired, high frequency vibrations at high g-forces may propagate through the gun and to adjacent tools. Once more, even after the primary event of firing, secondary ‘aftershock’ may ensue as the gun assembly is thrown about the well, rattling against the casing and any other downhole equipment.
The cumulative effect of this gun shock may be to damage the overall gun assembly beyond repair after only a single use. For example, electronics of assembly tools are likely to suffer solder joint and circuitry damage through both the initial wave of shock and subsequent downhole aftershock. With this in mind, the gun is often limited in terms of length and diameter so as to minimize the amount of shock damage to the overall assembly. Specifically, reusable perforating guns are generally limited to under about 2½ inches in diameter with a range or length spanning well under 20 or so perforating ports. These limitations constrain the total amount of explosive energy that the gun utilizes during any given perforating application. Thus, gun assembly damage attributable to gun shock may be kept to a minimum.
Of course, placing constraints on the gun as noted above also limits operator application options when utilizing the gun assembly. That is, it stands to reason that keeping the gun at or below 2½ inches in diameter in order to effectively limit the amount of gun shock also limits the perforating application itself. So, for example, an operator may seek a variety of application options in order to enhance perforation depth, profile or other characteristics. However, to the extent that these options would require a larger amount of explosive or different shaped charge profile than may be accommodated by a 2½ inch diameter gun, such options would be unavailable.
Compounding matters is the fact that the described constraints are not full proof. That is, placing such dimensional limitations on the gun is directed at preventing damage to adjacent gun assembly tools, thereby allowing the gun to be continually reused. However, the overall assembly continues to suffer some degree of shock related damage over time, regardless of these dimensional limitations. Thus, as a practical matter, for sake of ensuring reliability, it is unlikely that the gun would be utilized more than 100 times or so before a complete redressing of the assembly. The end result is a gun of significantly intentional limited capabilities that is still going to require a workover at some point.
With these gun limitations in mind, other efforts have been undertaken to help address the issue of gun shock. For example, certain shock absorber-like tools have been developed for incorporation into the gun assembly. Thus, in theory, the gun may be larger or of more flexible dimensions to allow for greater explosive energy during perforating, yet with gun shock mitigated by the shock absorber tool.
Unfortunately, shock absorber tools may be constructed of internal metal coils or springs that are unlikely to remain reliably effective after a single firing of the gun. As a result, redress of the assembly is required after every perforating application. That is, instead of being unable to reuse the assembly due to damaged electronics, reusability is now compromised due to the need to replace a shock absorber. Similarly, efforts have been undertaken to anchor the gun to the well casing during perforating to minimize assembly damage. However, this is likely to lead to casing damage. Once again, a degree of assembly damage of one type is likely to be exchanged for damage to another equipment feature. All in all, the operator is ultimately left with the undesirable option of deciding whether to compromise such equipment features or to use a smaller gun and compromise perforating application options.